 Now blood types are a phenotype that is caused by multiple alleles multiple alleles Contribute to the phenotypes that you see when we're talking about blood typing I'm gonna start by Explaining to you what blood typing is like what is your blood type and I if we were if we were sharing space I totally would ask you if anybody knows your blood type I try to give blood as often as possible It's the easiest form of organ transplant Because I just remake the blood that I give away every eight weeks Which is awesome, and it's super beneficial to folks who need blood So I this is super interesting, but most of us or many of us don't know our blood type and don't really know What blood typing is so let's? look at What are what it was what is blood type? Let's start with the phenotype for blood and I love you and I have to draw this it doesn't matter how many times I have talked about blood typing I Have to draw my blood cells in order to remember the story of What causes the blood type phenotype? We have four possible phenotypes when it comes to blood type and I say we have four possible phenotypes if anybody out there is like a blood-giving Hero you probably know that there actually is another thing involved in blood typing I'm not gonna talk about that other thing I'm gonna just stick to this but look at this We have type a blood Type do I have to write type every time or can I say type B? Type a B and type O So you may know what the thing is that I'm missing that would increase the number of possible phenotypes we have here It's the RH factor and the RH factor adds a plus or a minus to your blood type So actually and I I said I wasn't gonna do this, but I can't help it a Type a blood can be a positive or a negative Where the positive and the negative piece is the RH factor? For some reason they don't use RH factor in Genetics problems, and I don't know why because I have heard that it is coded for by a gene We're just gonna leave that Over there for we can talk about it when we do physio and come take physio with me because it's really fun to talk about blood type in that class so If you hear about RH factors or pluses and negatives, that's what it it means But what is the actual phenotype of a type a blood human? Well, they have these things called antigens Embedded in their some membranes think about this these antigens are Proteins and I make them with little a's on the end so that I can remember that those are a antigens and Antigens are just proteins Which means? How do we get proteins home kids? Proteins are coded for by genes So we need a gene the blood type gene to Tell us What kind of antigens to build? Proteins to embed in the cell membrane of a red blood cell What kind of antigens do you anticipate are found in type B blood? It was an easy one wasn't it? Blood typing is easy Please tell my physio students that it is easy It's not so easy, but that's okay. We will if it makes you feel like it's easy We will be very happy about that. What about type A B blood? You are correct because I can hear you We have both a and B Antigens embedded in the cell membrane and what about type O? What do you think is going on there? Hmm that that is going on there with type O blood. There are no antigens embedded in the cell membrane So the next question now we're talking about multiple alleles blood typing the A B blood types are coded for by one gene But all of our other situations have had two alleles right we've had a recessive leal and a dominant allele Well in the case of blood types, we actually have three possible alleles and I'm going to throw those Possible alleles down here. I'm going to throw the possible alleles way down here The gene I have no idea why is called the I gene cool and The I a allele codes for a antigens to be embedded in the cell membrane The Sun is coming out. Can you tell that the Sun is coming out? And it's like there's raindrops coming out of the redwood trees right now, and I'm like Super pretty out there and we're talking about blood typing, which is like my favorite thing. Oh Everything's my favorite thing, huh? What other allele if you had to guess another allele? What's another allele? the I B allele look at how I'm making the The Different alleles I've got the gene and The leal I'm doing like this little subscript. I'm doing capital eyes. What does that tell you hint hint? There are no hints on here for what I'm trying to tell you it was in the last lecture that your hint is Is that the end of the story? No, because of course we have a recessive I allele So we have there is a recessive I allele possible now Push pause you can totally do this What do you think predict the possible? Genotypes that give rise to each one of these phenotypes, so I'm gonna make you a chart genotypes Because there's gonna be multiple genotypes and once we do the genotypes you will see How this is actually an example of co-dominance. I Gave it away We do have multiple alleles. That's what we're talking about today, but you'll see anyway the co-dominance part Okay, guess the genotypes You pushed pause now you're gonna check yourself and see if you're right Well, if we have a antigens, I'm assuming that the I a allele is Necessary in order to get type A blood and I am assuming correct now. I could be homozygous I a That makes sense that that would lead to a Full expression of type A blood What's another possibility? Gotta have the I a you could have the little I recessive allele and still fully express Complete dominance in this mmm. I got to be careful of that In this case this heterozygote is fully expressing the a type A blood Okay, but we have two possible genotypes That's gonna lead to some complicated problems that you're gonna solve. Okay, what about B? What are our possible genotypes that lead to type B blood? Uh-huh, I Know that you knew that or I Know you knew that too Good job What about a B blood? What are you gonna do? Gotta have the I a to give rise to the a antigens Gotta have the I B to give rise to the B antigens. This is why blood typing is an example of co-dominance because you fully express a Type A blood and type B blood at the same time hence type a B blood What is the genotype of Someone who has type O blood Homozygous recessive no antigens on their red blood cells How you feel about that? That is that's super easy That's super clear The only thing that's weird about this is now we have three possible alleles to pick from and Our dominant alleles express Co-dominantly so they share the load and they're both fully expressed. It's not like you have sort of a blood and sort of B blood that would be incomplete dominance like you have this this Intermediate phenotype that's not what you have you have both you are functionally a and B and they call it a B blood Okay, how are you feeling? Be nice to yourself We're gonna keep this exact same picture and in the next section. We're gonna talk about a concept called epistasis Here we're looking at all the different ways that we can have complexity There's a phenomenon called called epistasis that we can see in blood typing that leads to phenotypic complexity That can be quite unexpected